1. Field of the Invention
The present invention relates to an image forming apparatus for forming images on a photosensitive body by allowing a light beam to be scanned and exposed thereon and, more particularly, to an image forming apparatus for receiving a light beam from light detecting means and generating a control signal required for image formation.
2. Related Background Art
Hitherto, an apparatus of the above type has a scanning optical system formed of a polygon mirror, an image forming optical system (including a f.theta. lens) or the like for allowing a light beam emitted from a semiconductor laser to be scanned onto a photosensitive body, which image forming optical system comprises first light detecting means for generating a timing signal in the direction of the main scanning in response to the reception of the light beam scanned by the scanning optical system when a non-image formed area on the photosensitive body is being scanned and second light detecting means for receiving a light beam to adjust the focus of the light beam when a non-image formed area on the photosensitive body is being scanned. The first and second light detecting means detect a light beam independently of each other so that an image is formed and the focus is controlled.
Therefore, a plurality of means for detecting a light beam are required for each object to be detected, causing a problem in that the cost of detection circuits is increased.